1. Field of the Invention
The present invention relates to a communication apparatus for direct communication between networks of different types (Heterogeneous Networks), and more particularly to a communication apparatus which removes the necessity of a gateway for converting data into data formats suitable for different types in the heterogeneous networks to remove a transmission delay factor and enable real-time speech and data communication.
2. Discussion of Related Art
Currently, a gateway is disposed between a public switched telephone network (PSTN) and an ultra-high frequency (UHF)-amplitude modulation (AM) network, which are different types of heterogeneous networks, for speech communication or general data communication between the networks. Pieces of speech data, general data, etc. received from the respective networks are converted and processed according to predetermined data standards at the gateway. The data standards are defined in the respective networks, and the pieces of converted and processed data are transmitted to users in the networks.
FIG. 1 shows a constitution of a conventional system for data communication between a PSTN and a UHF-AM network.
Referring to FIG. 1, the data communication system between the PSTN and the UHF-AM network includes a PSTN telephone 110, a terminal 120 for data transmission, and a modem 130 present in the PSTN, a gateway 140 relaying data communication, and a radio 150, a handset 160, and a terminal 170 for data transmission present in the UHF-AM network.
Speech communication is performed in the system shown in FIG. 1 as follows. When a user wants to send speech data through the PSTN telephone 110, the PSTN telephone 110 converts the corresponding speech data into a pulse code modulation (PCM) signal according to the PSTN and transmits the PCM signal to the gateway 140. The gateway 140 converts the transmitted PCM signal into an AM signal and then wirelessly transmits the AM signal to the user radio 150. The transmitted AM signal is demodulated by the radio 150. The demodulated signal is transferred to a user through the handset 160. This is a description of a case in which speech is transmitted from the PSTN to the UHF-AM network, and speech transmission in the reverse direction is performed in the same way.
Also, when secure speech communication is performed, an information security scheme (cryptographic equipment, e.g., a scrambling method) can be applied to the PSTN telephone 110 to perform secure communication with the gateway 140. At this time, at the gateway 140, a transmitted encryption data is reprocessed (decrypted and then encrypted again), and the reprocessed data is wirelessly transmitted to the user radio 150. The user can receive the data through the handset 160.
Meanwhile, data communication is performed as follows. Data input through the terminal 120 for data transmission in the PSTN is transmitted to the gateway 140 through the PSTN modem 130. The terminal 120 for data transmission may be a personal computer (PC) or a terminal dedicated to data transmission other than a PC. The gateway 140 amplitude-modulates the transmitted data and transmits the amplitude-modulated data to the radio 150 present in the UHF-AM network, and the data transmitted to the radio 150 is demodulated and transferred to the user through the terminal 160 for data transmission. This is a description of a case in which data is transmitted from the PSTN to the UHF-AM network, and data transmission in the reverse direction is performed in the same way.
Also, when secure data communication is performed, data to which an information security scheme is applied by the terminal 120 for data transmission in the PSTN may be transmitted to the gateway 140 through the modem 130, or data input through the terminal 120 for data transmission may be transmitted to the gateway 140 with an information security scheme applied by the modem 130. The terminal 120 for data transmission and the gateway 140 perform secure communication in the former method, and the modem 130 and the gateway 140 perform secure communication in the latter method. An information security scheme (cryptographic equipment, e.g., the scrambling method) suitable for the UHF-AM network is applied to the data transmitted to the gateway 140, and the data is transmitted to the radio 150 present in the UHF-AM network. At this time, an information security scheme may be applied to the terminal 120 for data transmission itself in the UHF-AM network for the sake of secure communication between the gateway 140 and the terminal 170 for data transmission, or a wireless channel information security scheme (an analog scrambling scheme) may be employed at the gateway 140 for the sake of secure communication between the gateway 140 and the radio 150.
Speech data or general data is converted into a data format appropriate for each network while passing through a gateway. At this time, the speech data or general data is inevitably transmitted with a delay factor caused by the conversion. The conversion becomes a delay factor in speech communication which must be performed in real time, and requires an additional modem suitable for each network for the sake of data transmission.
Also, when secure communication is performed, an information security scheme suitable for a PSTN network must be reprocessed (decrypted and then re-encrypted) according to an information security scheme suitable for UHF-AM network at a gateway. Thus, the gateway inevitably has security vulnerability.
Furthermore, separate information security schemes are required for speech and data.